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How would a white light look in a universe where red light is the brightest?

  1. Aug 10, 2011 #1
    How do I start "building" a universe in which red light radiation is the highest wavelenght radiation possible?

    I was wondering, if I lived in a universe in which red light is the "most powerfull" source of radiation, would I be able to detect a, for example, bright white light shining through my universe? or would it be impossible for me to build instruments able to do that?If so, would it appear to me as "black"?

    If energy is related to mass, than the highest source of energy in a certain type of universe dipends on the highest possible mass/space in said universe, right?
    If so, does the limit of m/s (untill the object colapses to form a black hole) dipend on the composition of the elements, atoms or elementary particles...?
  2. jcsd
  3. Aug 10, 2011 #2
    Stream of consciousness does not really fit well in physics, particularly if it doesn't make sense. What, precisely, are you trying to say/ask in your first post to this forum?
  4. Aug 11, 2011 #3
    sorry for being a bit unclear...
    Well, my first question would be "what determines the shortest wavelenght possible for electromagnetic radiations?". I mean, gamma rays are the highest energy ones; Is there a limit to the energy they can carry? If so, what does determine this limit?

    Atom decay produces low energy gamma rays, right? and, please correct me if I'm wrong, the more mass and the denser the object producing it, the higher in energy the rays are...up to the gamma ray bursts produced by hypernovas collapsing into forming black holes...

    Is there a relation between density and electromagnetic radiation? and is there a limit to the energy of electromagnetic radiation we can theoretically detect?

    Finally, would we be able, even just in theory, to build instruments capable of deteting electromagnetic radiation of wavelength many times shorter than Gamma Rays?
  5. Aug 12, 2011 #4
    The only way I know to derive a maximum frequency for electromagnetic radiation is by assuming that the energy of a photon is given by the quantum law E=hν and is confined within the wavelength of the photon considered in the context of general relativity. Since this would combine a quantum theory with a non-quantum theory, its results may not apply in extreme cases where a quantum formulation of gravity would be necessary. That being said, there is a frequency beyond which if two such photons were collided with each other they would collapse into a black hole. This frequency is that corresponding to each photon having an energy equal to half the http://en.wikipedia.org/wiki/Planck_energy" [Broken] can be large even for small changes in distance from the object).
    NASA's website on the http://www.nasa.gov/mission_pages/GLAST/spacecraft/index.html" [Broken] could detect the particle shower that would result if a sufficiently powerful gamma ray hit an atom in the upper atmosphere. I know of no limits on the energy of gamma rays that could be detected in this way (lower than the planck energy). However, I am not aware of any gamma rays that have been detected in this manner. Note: "gamma ray" describes a region of the electromagnetic spectrum with a somewhat arbitrary lower limit (the dividing line between gamma rays and x-rays is not universally agreed upon) and no upper limit (regarding the frequency/energy of the light).

    If we perceived photons with frequency corresponding to the planck energy as red, and had a similar range of vision (approximately a factor of 1.5 in frequency centered on green ~550nm, so let us say a factor of 1/4 below the highest frequency we might call red), we would see a bright source of "white" light as red (since any photons above the planck energy would collapse into black holes upon interaction with matter). However, I don't know how one would model such a hypothetical universe in a physically reasonable manner.
    Last edited by a moderator: May 5, 2017
  6. Aug 12, 2011 #5
    Imagin I'm able to "build" a small,dense, uniform cloud of dust, made up of the simpliest particles possible. ( lets forget for a moment the limits to how small i can get..)
    Now, if I shine a light on it,specifically tuned up to create a system that is turbulent at "very" microscopical scales, but quite linear at macroscopical ones, the cloud will start to heat up; the heat will make the particles move, faster and faster, collide with each other etc.. the cloud then will start to expand...at the same time gravity will start to pull the particles together forming bigger and bigger systems of particles...now, assume Ive done my calculations right, everything went as I wanted to...lets skip a few thousand years...I have created a universe much smaller than our own, but still "functioning". This universe,though, is too small, the elements are not heavy enough, there is not enaugh energy etc, to produce elecromagnetic radiations of the sort of the one I'm using to "heat IT up";
    My light is still shining on this cloud, still increasing this universe's energy.
    Now, imagin a little me on a little planet in this small universe. Would he be able to "see", detect, my light? wouldn't just appear to him, studing his universe, that his universe is powered by some sort of "dark energy" he can't see or detect? since my light is always been there, and it is so much out of the reach of his instrments in terms of how it is produced, and the "position" in the electromagnetic spectrum it occupies, etc, wouldn't it appear to him of the same "color" of what he considers "empty space"? Would it be possible that in this universe, in some spots matter gathered at just about enaugh densities to actually produce the sort of energy I am using; but considering that if this universe is permeated with this energy, and that if this energy is undetectable for the little me living there, since it is the same "colour" of the empty space (that HE would call black), wouldn't He "see" this spots in space as Black Holes"? (does it make sense.?)
    My second question would be, wouldn't He work out some sort of "general relativity" to explain how his universe works on macroscopical scales, and some sort of "quantum mechanics" to explain the microscopical events, since it is a turbulent system?
    PS. If I'm talking rubbish, just say so...
  7. Aug 12, 2011 #6
    Assuming his universe works something like ours, I don't see why he couldn't detect the light from outside the matter filled part of his universe. If you are referring to photons with enough energy to collapse into black holes upon interaction with matter, the black holes formed thereby would require a theory of quantum gravity (QG) to be described accurately (which we don't have yet (at least not one that has been experimentally tested)). Also, I am not sure if there are any processes that could produce such high energy photons (as describing this would probably also require a theory of QG).

    In any case, I do not think this light could appear to him as having the "color of empty space" (space is transparent, not black). Light carries momentum and curves space-time (at least classically), so he would be able to detect it via the effects it has on matter around him (e.g., through cosmic-ray observatories or surveys of the distribution of matter in his universe). Light of equal intensity from every direction would push inward on the cloud until its pressure due to its increasing temperature reached equilibrium with the pressure of the light (the cloud would heat up to a temperature somewhat below that of the light since the cloud would also radiate, it would reach equilibrium with the net radiation flux). (Throughout this post I assume the cloud is small/old enough for light to have crossed it many times in the history of your universe.)

    If you are trying to explain black holes and dark energy as products of an external source of light, this does not match what is observed. Surveys of the distribution of matter in the universe indicate that it is uniform on scales larger than a few hundred million light-years (all the way up to the cosmic microwave background, which is as far back in time as we will ever be able to see with light). Dark energy is causing the universe to expand at an increasing rate, contrary to what would be observed in your universe. Natural black holes (formed by the collapse of stars, etc.) do not have much in common with electromagnetic radiation (in particular they do not usually move (locally) at near the speed of light). As far as the possible black holes produced by the interaction of the light with matter, without a theory of QG I cannot say what they would look like (since I don't know if they would even exist for a noticeable period of time).
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